I've looked into this topic before also and I haven't found any real clear answers on this, as it relates to speed of draw. I've read Jordan and John Bianchi's book on gunleather. The topic is discussed slightly but I found no real answers.

I think that if you carry a pistol behind the hip, there is no doubt that the cant forward makes it easier to aquire the grip. Additionally, if you have a longer barrel and ride in a car all day, I think the cant forward is advantageous for both draw and comfort.

One other point is that if you carry a longer barreled firearm, like a 5" revolver, I think that not only is the pistol more concealable since the hoslter doesn't hang as low when canted, (plus butt is less likely to protrude back), but I think that you can clear the barrel quicker from the front of the holster, since when canted, the front opening is lower. I don't think you have to pull the pistol as high up to clear leather.